Initiation of propellant decomposition



Aug. 11, 1953 4 H. MAISNER INITIATIONV OF PROPELLANT DECOMPOSITION Filed March 5, 1948 IN VEN TOR.

HER/MAN MASVER ATTORVEY Patented Aug. ll, 1953 INITIATION OF 'PROPELLANT DECOMPOSITION Herman Maisnr,.pLos Angeles; Calif assigncr,

: by mesneassignments, to Aerojet-General Cor- ...pora tion,.: Cincinnati, lio,. a corporatio .of

" Ohio Application March 5, 1948,"? Serial'No.i-13;106

, 3 fllaims. -l

This: ,invention reats to the ignitiont of propellant injectedrinto rocketmotors, :and ;has for its-*principal object to; provide apositive; sima, ple; :dependable and safe ;meansor-.initiating the :decomposition "or` combustion of :the propellant l which servesas fuel tor` themotor.

i %Rockets and 'rocket: motors :operated by liquid propellant generally comprise. a ;reaction cham- Some liquidpropellants; ;suchas nitrop-arafins,

,are particularly desirable oroperating, a ;rocket gmotor, ;ass they ,areself comhustible :because they :contain: the oxygen requiredor. .theirgdecom- .position. :The nitroparain most commonly used has -been mononitromethane, e 'ordinarily called nitromethane;:and sometime a mixtureoinitromethane .and nitroethane :has been-used.

-It is highly udesi rable' that decomposition should startthesinstant that thenitroparafiin ;enters the reaction chamber; otherwise, an;undesirably large quantity; xofthe1 liquid -propellant (may: accumulate in the chamber before' it. starts `to decompose withthe result that' antexplosion ma-y result, when it :finally does react. Difiiculty has been experienced; -however in-` satisfactorily initiating the decomposition ofthe nitropatafiins when thefuel is; introduced into aco1d ;motor chamber.

.- A.-number of: expedientshave been; heretofore PIOPDSdr for insuri ;thegdecomposition ;of :the nitroparain at theinstantthat it is injectedinto the rocket motor chamber.: .onegoftthesejnvolves :the use of catalysts capable of assisting thede- ..composition of the nitroparaflin. Thesehowever.have not always proven as -rapdland certain in starting as is usually desired; 'and further- -more some of them requirea additionalignition e means. to start the reaction.

. 3 Another `expedient sometimes :used .is -to. :intro- ..luce the, nitroparaifininto a chamber having an .atmosphere gof: oxygen -gasand-igniting the mix- ..ture by. e suitablegelectrical ignition means such as ,a spark plug orthotspotq Theuse'of oxygenis -not alwaysdesirable, thowever; `due to the bulky containers necessaryzforostoringzthe oxyrgen ;under :pressurt and: alsobecause. of undesirably hi e p ratures that: may ;begenerated ,when the nitromethane:: is-rgdecomposed i in' the .presence. of oxy en.

Anothenexpedient heretofore usedforinitiating the recomposition of nitromethane has been 'to rspray a streamtiof nitromethane ;into areac- ,tion chamber intogw'hich there is also injecteda --mixture ofconcentrated hydrogen peroxide and concentratedsolution of calciuml permanganate.

fiThe'a'esultiIgreaction initiates the decomposition.

In accordance With my invention, I! providetan improvement in initiating the decompositionaof liquidnitroparaffins and 1 particularly &those nitroparaffinsa which are .classed .as monopropellants' I Carry out myginventionby 1usezof .a mass of a novel kinclof Catalyst which thave-found ,especially efiective.

' A eatureo. my invention is the-positionin of ;the Catalyst mass intthe reaction chamberat, a point where the stream of nitroparaffin from -the injector nozzleswill :strike it. I' prefern to :do

this by placing the-Catalyst ina small container ?within :the chamber, which may,-for :example be ta cylindenor the ,like,xhaving a mesh-likgwall,

such as a--metal-;screen or other& mesh-liketfabric. An alternative way would be to -place the Catalyst in some sort of-,suitable.capsule or the .like which would dissolve upon contact by the nitroparafiin.

, My inventionais also featured' by the use of an .especially effective catalystmaterial. This feature is based on my discovery that solid 'lithium aluminum tetrahydrde is-especiallyefiective in causing the. spontaneous decomposition of ,liquid nitroparafiins, forexample nitromethane, nitroethane, nitropropane,` nitrobutane etc., combin- `ations ofthe above asuch as mixtures of'nitromethane and nitroethane, as well as-liquid-tpoly- .nitroparaflinszsuch as tetranitromethane,` dinitroethane, etc. Theabove Catalyst-is particularly usefulwhen employed in intiating-thesdecomposition of theso-called monopropellant type .of nitroparafiin such as nitromethane .and dini- :troethane I have found thatwheneverthenitroparaffin touches thesurfaceof this catalyst,

thecatalyst .becomes extremely hot, evenito the .point of incandescence.

' Theimmediate localized heat, thus produced atthe Catalyst instantaneously initiates the decomposition of the nitroparafiin; 'and the resulting heatofthe decomposition will be sufiicient to insure-the continued decomposition of the nitroparaffin liquid which continues to 'enter the chamber.

' The foregoing and otherfeatures -of my invention will be better understood from the fol- 'lowngdetailed description and`-the 'accompany- ::ing ;drawing-in which:

Fig. 1 shows the cross section of a rocket motor provided with an ignitor charge according to my invention;

Fig. 2 shows a broken cross sectional View of the reaction chamber taken on the line 2-2 of Fig. 1; and

Fig. 3 shows a soluble form of capsule which may be used for the ignitor charge according to this invention.

Referring to the drawing there is shown a rocket motor operated by a liquid nitroparaffin injected into the chamber which is particularly designed for operation with nitromethane.

The motor comprises a combustion chamber ll, preferably cylindrical in shape. One end of the reaction chamber ll is provided With a closure cap [2 which is held in place by annular ring [3 having its lower surface shaped to conform with the Outline of cap !2. Ring 13 is secured to an annular shoulder !4 located at the upper edge of the reaction chamber Il by a plurality of bolts !5.

The opposite end of the reaction chamber I l is provided With a nozzle member !6, preferably of the De Laval type having a converging-diverging orifice 20, which is held securely in place by a retainer ring ll attached by a plurality of bolts !9 to a fiange [8 which is located at the lower end of the reaction chamber ll. A hollow cylindrical conduit 2! enters through the top of the closure member and extends inwardly into the closure a sufcient distance to communicate with a cavity 29. A plurality of Channels 23 radiate through the closure member from the cavity 29; and the outer ends of the channels 23 terminate in an annular groove 24, symmetrically located around the longitudinal axis of member 12. A number of injector orices 25 open from the groove into the reaction chamber Il; and the axes of these orifices are positioned at an angle with the longitudinal axis of closure member az so that the streams escaping through the injector intersect at a predetermined point within the reaction chamber.

It should be understood that the closure member just described is shown by way of example, rather than of limitation, and that some other suitable form of chamber or closure member or injector arrangement may be used instead, if desired.

The face of the closure member 12 opposite the one to which fitting 2I is attached, is provided with a threaded hole 26, preferably centrally positioned, which receives a stud 21. The stud is made preferably of some metal or alloy having a high heat resistance, and can be molybdenum or other metal capable of resisting the high temperature encountered in the reaction chamber while the motor is in operation.

A container 28 is Secured to the lower end of stud 21 and is filled with material which acts as a Catalyst for the injected propellant. The wall of the container is shown in the drawings as being metal screen; but it should be understood that some other suitable material of a more or less similar nature may be employed instead. The upper end of the cylinder is closed by a circular piece of solid metal 30 provided with a central hole which permits attachment to the stud 21; and the other end is closed by a disc of metal screen 31 which is Secured to the mesh cylinder by suitable means such as brazing, welding, soldering, etc.

The Catalyst container shown in the drawings is illustrated by way of example, and it should be the nitroparafn which strikes it.

understood that other suitable means of locating the catalyst charge in the proper position within the reaction chamber may be employed, if desired. Thus the metal screen may be replaced by a plastic screen or a capsule made of plastic or other material that is readily soluble in the nitroparaffin propellant. Fig. 3 shows such an arrangement of a soluble capsule 35 containing the Catalyst material, the capsule being Secured to the lower end of the stud 21 in place of the metal screen container 28 shown in Fig. 1. When the nitroparaflin strikes the capsule, the latter will immediately dissolve and the nitroparafiin will cause the catalyst to become incandescent the instant the liquid nitroparain touches its surface.

The Catalyst material which I have discovered to be most effective for use with the nitroparaifin propellant and particularly with nitromethane or a mixture of nitromethane and nitroethane, is lithium aluminum tetrahydride. The most effective way of putting this Catalyst material in the container within the chamber is in the form of solid particles. This will present a large number of surfaces which in their aggregate will have a large surface area, which will facilitate the incandescent heating effect of the Catalyst upon the liquid propellant inj ected against it.

In the operation of the motor, the liquid nitroparafn, for example, nitromethane, nitrcethane, nitropropane, nitrobutane; combinations of the above, such as mixtures of nitromethane and nitroethane as well as the liquid polynitroparaffins such as tetranitromethane, dinitroethane etc., is injected into the reaction chamber through the spray nozzle. The direction of the injector orices causes it to contact the catalytic mass and the Catalyst immediately becomes incandescent, developing heat enough to initiate the burning of This incandescence is accompanied by volatilization or burning away of the Catalyst, so that after the chamber temperature has risen sufficiently to cause sustained spontaneous combustion of the nitroparafiin, the Catalyst is decomposed.

The chamber temperature at which positive decomposition of nitromethane is insured is generally in the neighborhood of 500 F.; and above this temperature any nitromethane entering the chamber will be spontaneously decomposed even though the catalyst mass may have been completely volatilized or destroyed by the heat.

When the nitromethane thus decomposes spontaneously, the chamber temperature rises above 500 F., as the temperature that is generally developed by the stoichiometric decomposition of nitromethane into its molecular Components is generally in the order of 2500 K.

When the motor has ceased to operate, a new catalytic charge can be introduced into the chamber, thus preparing the motor for a subsequent start.

It will be recognized that by my invention I have provided a simple, inexpensive and positive means for intiating the decomposition of a monopropellant nitroparaffin such as nitromethane without the necessity of employing additive's which may undesirably sensitize the nitromethane or require the addition of outside oxidizer which materially increases the Weight and bulk of the installation. i

My ignitor does not require any outside starting means such as electrical sparks, oxygen or other previously known forms of initiators, since my Catalyst material substantially glows when coming in contact with the nitroparaffin and remains incandescent even though the nitroparaffin is sprayed thereon in large volumes.

A further advantage of my invention resides in the fact that a reiativeiy simple injection mechanism can be used since it need inject only the nitroparafin; and is not required also to im'ect some other substance to `aid starting.

I claim:

1. The method of nitiating the decomposition of a liquid nitroparan which oomprises spraying the liquid nitroparaffin on the surface of solid lithium aluminum tetrahydride.

2. The method of initiating the decomposition of a liquid monopropellant nitroparafiin in a rocket motor having a reaction chamber and an exhaust nozzle, which comprises spraying the nitroparaffin against a catalytic mass comprising solid lithium aiuminum tetrahydride within said reaction chamber.

3. The method of initiating the decomposition of nitromethane in a rooket motor having a reac-' tion chamber and an exhaust nozzle which comprises spraying the nitromethane against a catalytic mass comprising solid lithium aluminum tetrahydride within said reaction chamber.

HERMAN MAISNER.

References cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,301,044 Heard et ai Nov. 3, 1942 2,319,620 Mather May 18, 1943 2,380,391 Bates July 31, 1945 2,433,932 Stosick Jan. 6, 1948 2,433,943 Zwicky et al Jan. 6, 1948 2,438,261 Utterback Mar. 23, 1948 FOREIGN PATENTS Number Country Date 384386 France Feb. 3, 1908 

1. THE METHOD OF INITIATING THE DECOMPOSITION OF A LIQUID NITROPARAFFIN WHICH COMPRISES SPRAYING THE LIQUID NITROPARAFFIN ON THE SURFACE OF SOLID LITHIUM ALUMINUM TETRAHYDRIDE. 